"NASA isn't likely to have the necessary technology for at least a decade."
We have the necessary technology now.
Space is big, space does not care what shape/size your vehicle is (look at the space station, not exactly aerodynamic)
(in a nutshell)
To get to mars:
Ship: Build over a short time, in space, out of pieces you would bring up inside the shuttle. Once in space, the size/shape will not matter so make it a square if you want. Be sure to include a "docking" bay for your ship you use to get up / down on earth/mars. Ship must be double hulled.
Engine: Use standard engines/varient of system used to get to mars to get out off earth and into orbit, ship you build in space will be ion driven. Less fuel needed / with buildup you can get up to about 10x faster then conventional engines. (hence the "docking bay")
Food/water: Use a few trips earlier to take up your food and water and place it your ship.
Radiation protection: Double hulled ship, fill the space between with water or hydrogen. Alternativly ship can also be built to use an "electrostatic shield" for protection.
To land on mars: Use a standard shuttle initially to get to larger ship in earth orbit, however use a ship based on what was originally used for moon missions to get to your larger ship. Use a varient of the "lunar lander" such as was used on the moon, with chemical propulsion to land on mars and to get off.
Varient: Using the same type of "lunar lander" as used on the moon could be covered in "pillow inflation units" like those used to land the probes on mars, however this may be iffy on landing right side up. Little fuel to land needed.
To get off mars: Well pretty simple since you would be using a varient of the "lunar lander" you would use the chemical propellant in the lander to get off of mars.
Once off mars, redock with the larger ship, use ion drive for trip back.
Now this could theoretically require a few years to get to mars, however there has been some debate on this since ion engines, while not being useful for "planet to space" , once they are in place they are fairly good, but require a slow buildup to get to maximum speed.
Ion engine: http://nmp.nasa.gov/ds1/tech/ionpropfaq.html
This is of course a very basic outline, so feel free to add what YOU would use for any problems that you see.
Maybe a bunch of people who are NOT rocket scientist can come up with a viable plan.